如何在其他类中使用PDO连接? | 如何在其他类中使用PDO连接

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问题描述

我认为我在理解OOP的工作方式时遇到问题.我已经更改了它可以工作的代码，但这并不是我认为的正确方法.以下情况(不，我不是自己创建用户登录的，它实际上只是为了让本地开发人员更好地理解OOP):

I think I've a problem in understanding how OOP works. I already changed the code that it works, but it isn't the propper way I think. Following scenario (No, I'm not creating a userlogin by myself, its really just for local dev. to understand OOP better):

我有一个database.php文件:

I've a database.php file:

class Database {

    /* Properties */
    private $conn;
    private $dsn = 'mysql:dbname=test;host=127.0.0.1';
    private $user = 'root';
    private $password = '';

    /* Creates database connection */
    public function __construct() {
        try {
            $this->conn = new PDO($this->dsn, $this->user, $this->password);
        } catch (PDOException $e) {
            print "Error!: " . $e->getMessage() . "";
            die();
        }
        return $this->conn;
    }
}

所以在这个类中，我正在创建数据库连接，然后返回连接(对象?)

So in this class I'm creating a database connection and I return the connection (object?)

然后我有第二个类，著名的User类(实际上我没有使用自动加载功能，但是我知道):

Then I have a second class, the famous User class (actually I'm not using autoload, but I know about it):

include "database.php";

class User {
    /* Properties */
    private $conn;

    /* Get database access */
    public function __construct() {
        $this->conn = new Database();
    }

    /* Login a user */
    public function login() {
        $stmt = $this->conn->prepare("SELECT username, usermail FROM user");
        if($stmt->execute()) {
            while($rows = $stmt->fetch()) {
                $fetch[] = $rows;
            }
            return $fetch;
        }
        else {
            return false;
        }
    }
}

那是我的两个课.如您所见，没什么大不了的.现在，不要对函数名login感到困惑-实际上，我只是尝试从数据库中选择一些用户名和用户邮件并显示它们.我尝试通过以下方式实现这一目标:

So thatare my two classes. Nothing big, as you see. Now, don't get confued about the function name login - Actually I just try to select some usernames and usermails from database and displaying them. I try to achieve this by:

$user = new User();
$list = $user->login();

foreach($list as $test) {
    echo $test["username"];
}

问题来了.执行此代码时，出现以下错误消息:

And here comes the problem. When I execute this code, I get the following error message:

我不确定我是否真的了解导致此错误的原因.

And I'm not sure that I really understand what causes this error.

当我更改以下内容时，代码将运行良好:

将database.php中的$conn更改为public而不是private(我认为那很糟糕...?但是当它为private时，我只能在Database类内部执行查询，对吗?数据库类中的所有这些查询?我认为这很不好，因为在一个大型项目中，它将变得非常大..

Change $conn in database.php to public instead of private (I think thats bad...? But when its private, I can only execute querys inside of the Database class, I'm right? So should I put all these querys in the Database class? I think that's bad, because in a big project it will get become really big..)

第二个要做的更改是:在user.php文件中将$this->conn->prepare更改为$this->conn->conn->prepare.在这里，我真的不知道为什么.

And the second change I've to do is:Change $this->conn->prepare to $this->conn->conn->prepare in the user.php file. And here I've really no Idea why.

我的意思是，在user.php的构造函数中，我有一个$this->conn = new Database()，并且由于新数据库将返回DB类的连接对象，所以我真的不知道为什么必须再添加一个

I mean, in the constructor of the user.php I've a $this->conn = new Database() and since new Database will return me the connection object from DB class, I really don't know why there have to be a second conn->

推荐答案

您当前的课程非常没用.如果它为PDO添加了一些额外的功能，则创建数据库包装程序将是有意义的.但鉴于其当前代码，最好改用香草PDO.
无论哪种方式，都可以通过普通PDO或您的数据库类创建单个 $ db实例.
将其作为构造函数参数传递给每个需要数据库连接的类

your current class is rather useless. It would make sense to create a database wrapper if it adds some extra functionality to PDO. But given its current code, better to use vanilla PDO instead.
Either way, create a single $db instance from either vanilla PDO or your database class.
pass it as a constructor parameter into every class that needs a database connection

database.php:

<?php
$host = '127.0.0.1';
$db   = 'test';
$user = 'root';
$pass = '';
$charset = 'utf8';

$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$opt = [
    \PDO::ATTR_ERRMODE            => \PDO::ERRMODE_EXCEPTION,
    \PDO::ATTR_DEFAULT_FETCH_MODE => \PDO::FETCH_ASSOC,
    \PDO::ATTR_EMULATE_PREPARES   => false,
];
$pdo = new \PDO($dsn, $user, $pass, $opt);

user.php

<?php
class User {
    /* Properties */
    private $conn;

    /* Get database access */
    public function __construct(\PDO $pdo) {
        $this->conn = $pdo;
    }

    /* List all users */
    public function getUsers() {
        return $this->conn->query("SELECT username, usermail FROM user")->fetchAll();
    }
}

app.php

include 'database.php';
$user = new User($pdo);
$list = $user->getUsers();

foreach($list as $test) {
    echo $test["username"],"\n";
}

输出:

username_foo
username_bar
username_baz

查看我的(唯一合适的)PDO教程，以获取更多PDO详细信息.

Check out my (The only proper) PDO tutorial for more PDO details.

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